The dental pantograph is currently the primary instrument for measuring jaw motion. The pantograph provides motion envelope tracings on paper. Some models interface electronically with a computer for positional data processing. The pantograph device does not accurately measure the six-dimensional space of movement present between upper and lower jaws.
The pantograph device is cumbersome because it must be clamped to the patient's head, and thereby restricts complete freedom of movement and precludes measurements of normal jaw chewing and talking motions. It requires significant set up time and is very technique-sensitive. Because of these shortcomings, the pantograph is seldom used in actual practice except for very specialized reconstructive work.
Previous investigators have attempted to overcome the pantograph's deficiencies. These efforts have contributed to an evolutionary improvement in the technology and a better understanding of the clinical requirements. The following discussion, however, is limited to devices for measuring jaw motion and does not include more generalized instruments.
One such device uses a magnet placed in the mouth with sensors around the head. This device records only the three dimensions of translation and not rotation. Consequently, it is of limited value.
Another device uses fiber optics and custom semiconductor light sensitive arrays to measure the relative motion between the upper and lower jaw. This device requires a cumbersome apparatus to be worn by the patient which actually prevents measurements during normal oral activity. It also requires very expensive, custom semiconductor components which render it commercially impractical.
Another device, a Kinesiograph, uses magnets and pickup coils to display the mandible motion on an oscilloscope. This device requires the patient to wear an apparatus which precludes normal oral activity during testing. It suffers from linearity problems and presents a fleeting analog display that is difficult to analyze with a computer.
Another device uses two arrays of ultrasound devices, one held in the lower jaw with a jaw plate and the other strapped to the head. The ultrasound transmitters are pulsed sequentially. The sound signals are received at three points that define a plane. By measuring the transit time for the ultrasound signals, it is possible to determine the relative position of the transmitters and receivers. This device also suffers from the problem that an uncomfortable device must be held in the mouth which prevents normal oral activity. In addition, the electronic specifications for reliable and accurate operation are very demanding making it too costly. A number of other devices using light emitting diodes and various sensor arrangements have been tried. These devices add the benefit of real time measurement and have incrementally advanced the art but fail to achieve all the objectives of a useful instrument. In particular, these devices fail to achieve unencumbered oral freedom of movement during measurement or to provide accurate 3-dimensional measurement.
Baumrind et al., U.S. Pat. No. 4,836,778, have advanced the LED array method to the point where they are able to measure the movement of the cranium and lower jaw independently with respect to a reference and also to measure rotation and translation on all axes (six degrees of freedom). This device, however, still requires the patient to wear a harness of illuminated LEDs. It also requires significant set up and adjustment and a calibration process. The distance between the patient and the sensors must be kept constant after calibration. The sensors are subject to calibration shifts and can vary during the time of the test. With this method, a large part of the measurement function is passed onto the computer where specialized software processes the data.
There are other, more general, body motion tracking devices both in use and under development. These other devices are expensive and too generalized to be practical for the specific application to the mandible discussed here.
The present instrument provides a means to record and analyze jaw motion. It incorporates innovative techniques to obtain a level of performance not presently available. This performance will open the doors to clinical techniques not presently practical. In addition it may bring greater awareness of oral motor pathologies and may aid in the evolution of new clinical practices to treat these pathologies.
Those skilled in the art will appreciate the numerous possible applications for this invention. It is a tool that can provide detailed information where previously only imprecise information was available. Awareness of the usefulness of this information will grow with experience.
Therefore, it is an object of the present invention to provide an apparatus and method for collecting and recording data representative of jaw movement, including rotational and translational motion along each of three axes of a three dimensional Cartesian coordinate system.
Another object of the invention is to provide a computer generated simulation of the subject's jaw movement on a screen display, which can be analyzed and manipulated through the use of software.
Another object of the invention is to provide an apparatus and method for electronically producing a dental pantograph.
Another object of the invention is to provide an apparatus and method for electronically adjusting an articulator for diagnostic and/or therapeutic purposes.